Residual microstructure and damage geometry associated with high speed impact crater in Al ₂O ₃ and TiB ₂ particles reinforced 2024 Al composite

The resistance of Al ₂O ₃ + TiB ₂/2024Al composite to hypervelocity impact was tested by a two-stage light gas gun. The impact damage behaviors of the Al ₂O ₃ + TiB ₂/2024Al composite by different-sized Al projectiles with a velocity of 2.49 km/s and the residual microstructures associated with the crater impacted by a 1.2 mm aluminum projectile were investigated by transmission electron microscopy and high-resolution transmission electron microscopy. Both the diameters of craters at front face and spalling areas at back face increased with the aluminum projectile diameter. The diameter of perforation on the 2 mm thick Al ₂O ₃ + TiB ₂/Al composite target was zero when impacted by 1.2 mm aluminum projectile and it increased to 2.4 mm when the projectile diameter was 1.5 mm, indicating that the critical perforation diameter of the aluminum projectile was between 1.2 mm and 1.5 mm when the 2 mm thick Al ₂O ₃ + TiB ₂/Al composite target was impacted by 2.49 km/s aluminum projectiles. The diameter of perforation increases with the diameter of Al projectile. In addition, under each impact condition, the diameters of craters at front face were smaller than that of spalling areas at back face. Microstructure observations by transmission electron microscopy demonstrated four characteristics: stacking faults around TiB ₂ particle and dislocations within the TiB ₂ particle; twins in the Al ₂O ₃ particle; recrystal grains in 2024 Al matrix; and mixture of amorphous microstructure and nanograins in the matrix.